Electrically variable transmission having three planetary gear sets, a stationary member, three fixed interconnections and clutched input

ABSTRACT

The electrically variable transmission family of the present invention provides low-content, low-cost electrically variable transmission mechanisms including first, second and third differential gear sets, a battery, two electric machines serving interchangeably as motors or generators, up to five selectable torque-transfer devices and possibly a dog clutch. The selectable torque transmitting devices are engaged to yield an EVT with a continuously variable range of speeds (including reverse) and up to four mechanically fixed forward speed ratios. The torque transmitting devices and the first and second motor/generators are operable to provide five operating modes in the electrically variable transmission, including battery reverse mode, EVT reverse mode, reverse and forward launch modes, continuously variable transmission range mode, and fixed ratio mode.

TECHNICAL FIELD

The present invention relates to electrically variable transmissionswith selective operation both in power-split variable speed ratio rangesand in fixed speed ratios, and having three planetary gear sets, twomotor/generators and up to five torque transmitting devices.

BACKGROUND OF THE INVENTION

Internal combustion engines, particularly those of the reciprocatingpiston type, currently propel most vehicles. Such engines are relativelyefficient, compact, lightweight, and inexpensive mechanisms by which toconvert highly concentrated energy in the form of fuel into usefulmechanical power. A novel transmission system, which can be used withinternal combustion engines and which can reduce fuel consumption andthe emissions of pollutants, may be of great benefit to the public.

The wide variation in the demands that vehicles typically place oninternal combustion engines increases fuel consumption and emissionsbeyond the ideal case for such engines. Typically, a vehicle ispropelled by such an engine, which is started from a cold state by asmall electric motor and relatively small electric storage batteries,then quickly placed under the loads from propulsion and accessoryequipment. Such an engine is also operated through a wide range ofspeeds and a wide range of loads and typically at an average ofapproximately a fifth of its maximum power output.

A vehicle transmission typically delivers mechanical power from anengine to the remainder of a drive system, such as fixed final drivegearing, axles and wheels. A typical mechanical transmission allows somefreedom in engine operation, usually through alternate selection of fiveor six different drive ratios, a neutral selection that allows theengine to operate accessories with the vehicle stationary, and clutchesor a torque converter for smooth transitions between driving ratios andto start the vehicle from rest with the engine turning. Transmissiongear selection typically allows power from the engine to be delivered tothe rest of the drive system with a ratio of torque multiplication andspeed reduction, with a ratio of torque reduction and speedmultiplication known as overdrive, or with a reverse ratio.

An electric generator can transform mechanical power from the engineinto electrical power, and an electric motor can transform that electricpower back into mechanical power at different torques and speeds for theremainder of the vehicle drive system. This arrangement allows acontinuous variation in the ratio of torque and speed between engine andthe remainder of the drive system, within the limits of the electricmachinery. An electric storage battery used as a source of power forpropulsion may be added to this arrangement, forming a series hybridelectric drive system.

The series hybrid system allows the engine to operate with someindependence from the torque, speed and power required to propel avehicle, so the engine may be controlled for improved emissions andefficiency. This system allows the electric machine attached to theengine to act as a motor to start the engine. This system also allowsthe electric machine attached to the remainder of the drive train to actas a generator, recovering energy from slowing the vehicle into thebattery by regenerative braking. A series electric drive suffers fromthe weight and cost of sufficient electric machinery to transform all ofthe engine power from mechanical to electrical in the generator and fromelectrical to mechanical in the drive motor, and from the useful energylost in these conversions.

A power-split transmission can use what is commonly understood to be“differential gearing” to achieve a continuously variable torque andspeed ratio between input and output. An electrically variabletransmission can use differential gearing to send a fraction of itstransmitted power through a pair of electric motor/generators. Theremainder of its power flows through another, parallel path that is allmechanical and direct, of fixed ratio, or alternatively selectable.

One form of differential gearing, as is well known to those skilled inthis art, may constitute a planetary gear set. Planetary gearing isusually the preferred embodiment employed in differentially gearedinventions, with the advantages of compactness and different torque andspeed ratios among all members of the planetary gear set. However, it ispossible to construct this invention without planetary gears, as byusing bevel gears or other gears in an arrangement where the rotationalspeed of at least one element of a gear set is always a weighted averageof speeds of two other elements.

A hybrid electric vehicle transmission system also includes one or moreelectric energy storage devices. The typical device is a chemicalelectric storage battery, but capacitive or mechanical devices, such asan electrically driven flywheel, may also be included. Electric energystorage allows the mechanical output power from the transmission systemto the vehicle to vary from the mechanical input power from the engineto the transmission system. The battery or other device also allows forengine starting with the transmission system and for regenerativevehicle braking.

An electrically variable transmission in a vehicle can simply transmitmechanical power from an engine input to a final drive output. To do so,the electric power produced by one motor/generator balances theelectrical losses and the electric power consumed by the othermotor/generator. By using the above-referenced electrical storagebattery, the electric power generated by one motor/generator can begreater than or less than the electric power consumed by the other.Electric power from the battery can sometimes allow bothmotor/generators to act as motors, especially to assist the engine withvehicle acceleration. Both motors can sometimes act as generators torecharge the battery, especially in regenerative vehicle braking.

A successful substitute for the series hybrid transmission is thetwo-range, input-split and compound-split electrically variabletransmission now produced for transit buses, as disclosed in U.S. Pat.No. 5,931,757, issued Aug. 3, 1999, to Michael Roland Schmidt, commonlyassigned with the present application. Such a transmission utilizes aninput means to receive power from the vehicle engine and a power outputmeans to deliver power to drive the vehicle. First and secondmotor/generators are connected to an energy storage device, such as abattery, so that the energy storage device can accept power from, andsupply power to, the first and second motor/generators. A control unitregulates power flow among the energy storage device and themotor/generators as well as between the first and secondmotor/generators.

Operation in first or second variable-speed-ratio modes of operation maybe selectively achieved by using clutches in the nature of first andsecond torque transfer devices. In the first mode, an input-power-splitspeed ratio range is formed by the application of the first clutch, andthe output speed of the transmission is proportional to the speed of onemotor/generator. In the second mode, a compound-power-split speed ratiorange is formed by the application of the second clutch, and the outputspeed of the transmission is not proportional to the speeds of either ofthe motor/generators, but is an algebraic linear combination of thespeeds of the two motor/generators. Operation at a fixed transmissionspeed ratio may be selectively achieved by the application of both ofthe clutches. Operation of the transmission in a neutral mode may beselectively achieved by releasing both clutches, decoupling the engineand both electric motor/generators from the transmission output. Thetransmission incorporates at least one mechanical point in its firstmode of operation and at least two mechanical points in its second modeof operation.

“Compound split” means that neither the transmission input nor output isdirectly connected to a motor/generator. A compound split architectureincludes a mode with two mechanical points, each of which is attainedwhen one of the motor/generators reaches zero speed. This allows areduction in the size and cost of the electric motor/generator requiredto achieve desired vehicle performance. “Output split” means amotor/generator is directly connected to the input. This mode is usefulfor launching the vehicle. “Input split” means a motor/generator isdirectly connected to the output member. This is useful in capturingregenerative energy during braking and for providing torque assist tothe engine as needed.

U.S. Pat. No. 6,527,658, issued Mar. 4, 2003 to Holmes et al, commonlyassigned with the present application, discloses an electricallyvariable transmission utilizing two planetary gear sets, twomotor/generators and two clutches to provide input split, compoundsplit, neutral and reverse modes of operation. Both planetary gear setsmay be simple, or one may be individually compounded. An electricalcontrol member regulates power flow among an energy storage device andthe two motor/generators. This transmission provides two ranges or modesof electrically variable transmission (EVT) operation, selectivelyproviding an input-power-split speed ratio range and acompound-power-split speed ratio range. One fixed speed ratio can alsobe selectively achieved.

SUMMARY OF THE INVENTION

The present invention provides a family of electrically variabletransmissions offering several advantages over conventional automatictransmissions for use in hybrid vehicles, including improved vehicleacceleration performance, improved fuel economy via regenerative brakingand electric-only idling and launch, and an attractive marketingfeature. An object of the invention is to provide the best possibleenergy efficiency and emissions for a given engine. In addition, optimalperformance, capacity, package size, and ratio coverage for thetransmission are sought.

The electrically variable transmission family of the present inventionprovides low-content, low-cost electrically variable transmissionmechanisms including first, second and third differential gear sets, abattery, two electric machines serving interchangeably as motors orgenerators, and up to five selectable torque-transmitting devices.Additionally, a dog clutch may be provided. Preferably, the differentialgear sets are planetary gear sets, such as simple or compound (includingRavigneaux) gear sets, but other gear arrangements may be implemented,such as bevel gears or differential gearing to an offset axis.

In this description, the first, second, or third planetary gear sets maybe counted first to third in any order (i.e., left to right, right toleft, etc.).

Each of the three planetary gear sets has three members. The first,second or third member of each planetary gear set can be any one of asun gear, ring gear or carrier member, or alternatively a pinion.

Each carrier member can be either a single-pinion carrier member(simple) or a double-pinion carrier member (compound).

The input shaft is selectively connected with at least one member of theplanetary gear sets. The output shaft is continuously connected with atleast one member of the planetary gear sets.

A first interconnecting member continuously connects the first member ofthe first planetary gear set with the first member of the secondplanetary gear.

A second interconnecting member continuously connects the second memberof the first planetary gear set with the first member of the thirdplanetary gear set.

A third interconnecting member continuously connects the second memberof the second planetary gear set with the second member of the thirdplanetary gear set.

A fourth interconnecting member continuously connects a member of thefirst planetary gear set with a stationary member (ground/transmission).

A first torque transmitting device selectively connects a member of thefirst or second planetary gear set with the input member.

A second torque transmitting device selectively connects a member of thethird planetary gear set with another member of the first, second orthird planetary gear set or with the input member. The connection fromthe third planetary gear set to the input member may be achieved via thesecond interconnecting member.

A third torque transmitting device selectively connects a member of thesecond or third planetary gear set with another member of the first,second or third planetary gear set or with a stationary member(ground/transmission case).

A fourth torque transmitting device is connected in parallel with one ofthe motor/generators for selectively preventing rotation of themotor/generator.

An optional fifth torque transmitting device is connected in parallelwith the other of the motor/generators for selectively preventingrotation thereof.

The first motor/generator is mounted to the transmission case and isconnected either continuously or selectively via a dog clutch to amember of the first, second or third planetary gear set. The firstmotor/generator may also incorporate offset gearing. The dog clutch, ifpresent, allows the first motor/generator to be switched between a pairof members on the first, second or third planetary gear sets. The dogclutch may reduce clutch spin losses, and allows motor/generatoroperation at low speeds throughout the operating range of thetransmission. The dog clutch may be replaced by a pair of conventionaltorque transfer devices.

The second motor/generator is mounted to the transmission case and isconnected either continuously or selectively via a dog clutch to amember of the third planetary gear set. The second motor/generatorconnection may incorporate offset gearing. The dog clutch, if present,allows the second motor/generator to be switched between a pair ofmembers on the first, second or third planetary gear sets. The dogclutch may reduce clutch spin losses, and allows motor/generatoroperation at low speeds throughout the operating range of thetransmission. The dog clutch may be replaced by a pair of conventionaltorque transfer devices.

The selectable torque transmitting devices are engaged in combinationsto yield an EVT with a continuously variable range of speeds (includingreverse) and up to four mechanically fixed forward speed ratios. A“fixed speed ratio” is an operating condition in which the mechanicalpower input to the transmission is transmitted mechanically to theoutput, and no power flow (i.e. almost zero) is present in themotor/generators. An electrically variable transmission that mayselectively achieve several fixed speed ratios for operation near fullengine power can be smaller and lighter for a given maximum capacity.Fixed ratio operation may also result in lower fuel consumption whenoperating under conditions where engine speed can approach its optimumwithout using the motor/generators. A variety of fixed speed ratios andvariable ratio spreads can be realized by suitably selecting the toothratios of the planetary gear sets.

Each embodiment of the electrically variable transmission familydisclosed has an architecture in which neither the transmission inputnor output is directly connected to a motor/generator. This allows for areduction in the size and cost of the electric motor/generators requiredto achieve the desired vehicle performance.

The torque transmitting devices, and the first and secondmotor/generators are operable to provide five operating modes in theelectrically variable transmission, including battery reverse mode, EVTreverse mode, reverse and forward launch modes, continuously variabletransmission range mode, and fixed ratio mode. The transmission of thepresent invention may also include a mechanical or fixed reverse ratio.This is useful for meeting reverse gradeability requirements and alsofor cold-weather operation when the electrical torque assist may not beavailable due to poor battery operation.

The above features and advantages, and other features and advantages ofthe present invention are readily apparent from the following detaileddescription of the best modes for carrying out the invention when takenin connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a schematic representation of a powertrain including anelectrically variable transmission incorporating a family member of thepresent invention;

FIG. 1 b is an operating mode table and fixed ratio mode table depictingsome of the operating characteristics of the powertrain shown in FIG. 1a;

FIG. 2 a is a schematic representation of a powertrain having anelectrically variable transmission incorporating another family memberof the present invention;

FIG. 2 b is an operating mode table and fixed ratio mode table depictingsome of the operating characteristics of the powertrain shown in FIG. 2a;

FIG. 3 a is a schematic representation of a powertrain having anelectrically variable transmission incorporating another family memberof the present invention;

FIG. 3 b is an operating mode table and fixed ratio mode table depictingsome of the operating characteristics of the powertrain shown in FIG. 3a;

FIG. 4 a is a schematic representation of a powertrain having anelectrically variable transmission incorporating another family memberof the present invention;

FIG. 4 b is an operating mode table and fixed ratio mode table depictingsome of the operating characteristics of the powertrain shown in FIG. 4a;

FIG. 5 a is a schematic representation of a powertrain having anelectrically variable transmission incorporating another family memberof the present invention;

FIG. 5 b is an operating mode table and fixed ratio mode table depictingsome of the operating characteristics of the powertrain shown in FIG. 5a;

FIG. 6 a is a schematic representation of a powertrain having anelectrically variable transmission incorporating another family memberof the present invention; and

FIG. 6 b is an operating mode table and fixed ratio mode table depictingsome of the operating characteristics of the powertrain shown in FIG. 6a.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIG. 1 a, a powertrain 10 is shown, including anengine 12 connected to one preferred embodiment of the improvedelectrically variable transmission (EVT), designated generally by thenumeral 14. Transmission 14 is designed to receive at least a portion ofits driving power from the engine 12. As shown, the engine 12 has anoutput shaft that serves as the input member 17 of the transmission 14.A transient torque damper (not shown) may also be implemented betweenthe engine 12 and the input member 17 of the transmission.

In the embodiment depicted the engine 12 may be a fossil fuel engine,such as a diesel engine which is readily adapted to provide itsavailable power output typically delivered at a constant number ofrevolutions per minute (RPM).

Irrespective of the means by which the engine 12 is connected to thetransmission input member 17, the transmission input member 17 isoperatively connected to a planetary gear set in the transmission 14. Anoutput member 19 of the transmission 14 is connected to a final drive16.

The transmission 14 utilizes three differential gear sets, preferably inthe nature of planetary gear sets 20, 30 and 40. The planetary gear set20 employs an outer gear member 24, typically designated as the ringgear. The ring gear member 24 circumscribes an inner gear member 22,typically designated as the sun gear. A carrier member 26 rotatablysupports a plurality of planet gears 27 such that each planet gear 27meshingly engages both the outer, ring gear member 24 and the inner, sungear member 22 of the first planetary gear set 20.

The planetary gear set 30 also has an outer gear member 34, often alsodesignated as the ring gear, that circumscribes an inner gear member 32,also often designated as the sun gear member. A plurality of planetgears 37 are also rotatably mounted in a carrier member 36 such thateach planet gear member 37 simultaneously, and meshingly, engages boththe outer, ring gear member 34 and the inner, sun gear member 32 of theplanetary gear set 30.

The planetary gear set 40 also has an outer gear member 44, often alsodesignated as the ring gear, that circumscribes an inner gear member 42,also often designated as the sun gear. A plurality of planet gears 47are also rotatably mounted in a carrier member 46 such that each planetgear member 47 simultaneously, and meshingly, engages both the outer,ring gear member 44 and the inner, sun gear member 42 of the planetarygear set 40.

A first interconnecting member 70 continuously connects the carriermember 26 of the planetary gear set 20 with the ring gear member 34 ofthe planetary gear set 30. A second interconnecting member 72continuously connects the sun gear member 22 of the planetary gear set20 with the carrier member 46 of the planetary gear set 40. A thirdinterconnecting member 74 continuously connects the sun gear member 32of the planetary gear set 30 with the sun gear member 42 of theplanetary gear set 40. A fourth interconnecting member 76 continuouslyconnects the ring gear member 24 with the transmission housing 60.

The first preferred embodiment 10 also incorporates first and secondmotor/generators 80 and 82, respectively. The stator of the firstmotor/generator 80 is secured to the transmission housing 60. The rotorof the first motor/generator 80 is secured to the sun gear member 42 ofthe planetary gear set 40.

The stator of the second motor/generator 82 is also secured to thetransmission housing 60. The rotor of the second motor/generator 82 issecured to the ring gear member 44 of the planetary gear set 40.

A first torque transmitting device, such as input clutch 50, selectivelyconnects the carrier member 36 of the planetary gear set 30 with theinput member 17. A second torque transmitting device, such as clutch 52,selectively connects the sun gear member 42 of the planetary gear set 40with the carrier member 46 of the planetary gear set 40. A third torquetransmitting devise, such as clutch 54, selectively connects the ringgear member 34 of the planetary gear set 30 with the carrier member 36of the planetary gear set 30. A fourth torque transmitting device, suchas the brake 55, is connected in parallel with the motor/generator 80for selectively braking rotation thereof. A fifth torque transmittingdevice, such as brake 57, is connected in parallel with themotor/generator 82 for selectively braking rotation thereof. The first,second, third, fourth and fifth torque transmitting devices 50, 52, 54,55 and 57 are employed to assist in the selection of the operationalmodes of the hybrid transmission 14, as will be hereinafter more fullyexplained.

The output drive member 19 of the transmission 14 is secured to carriermember 26 of the planetary gear set 20.

Returning now to the description of the power sources, it should beapparent from the foregoing description, and with particular referenceto FIG. 1 a, that the transmission 14 selectively receives power fromthe engine 12. The hybrid transmission also receives power from anelectric power source 86, which is operably connected to a controller88. The electric power source 86 may be one or more batteries. Otherelectric power sources, such as fuel cells, that have the ability toprovide, or store, and dispense electric power may be used in place ofbatteries without altering the concepts of the present invention.

General Operating Considerations

One of the primary control devices is a well known drive range selector(not shown) that directs an electronic control unit (the ECU 88) toconfigure the transmission for either the park, reverse, neutral, orforward drive range. The second and third primary control devicesconstitute an accelerator pedal (not shown) and a brake pedal (also notshown). The information obtained by the ECU from these three primarycontrol sources is designated as the “operator demand.” The ECU alsoobtains information from a plurality of sensors (input as well asoutput) as to the status of: the torque transfer devices (either appliedor released); the engine output torque; the unified battery, orbatteries, capacity level; and, the temperatures of selected vehicularcomponents. The ECU determines what is required and then manipulates theselectively operated components of, or associated with, the transmissionappropriately to respond to the operator demand.

The invention may use simple or compound planetary gear sets. In asimple planetary gear set a single set of planet gears are normallysupported for rotation on a carrier member that is itself rotatable.

In a simple planetary gear set, when the sun gear is held stationary andpower is applied to the ring gear of a simple planetary gear set, theplanet gears rotate in response to the power applied to the ring gearand thus “walk” circumferentially about the fixed sun gear to effectrotation of the carrier member in the same direction as the direction inwhich the ring gear is being rotated.

When any two members of a simple planetary gear set rotate in the samedirection and at the same speed, the third member is forced to turn atthe same speed, and in the same direction. For example, when the sungear and the ring gear rotate in the same direction, and at the samespeed, the planet gears do not rotate about their own axes but ratheract as wedges to lock the entire unit together to effect what is knownas direct drive. That is, the carrier member rotates with the sun andring gears.

However, when the two gear members rotate in the same direction, but atdifferent speeds, the direction in which the third gear member rotatesmay often be determined simply by visual analysis, but in manysituations the direction will not be obvious and can only be accuratelydetermined by knowing the number of teeth present on all the gearmembers of the planetary gear set.

Whenever the carrier member is restrained from spinning freely, andpower is applied to either the sun gear or the ring gear, the planetgear members act as idlers. In that way the driven member is rotated inthe opposite direction as the drive member. Thus, in many transmissionarrangements when the reverse drive range is selected, a torque transferdevice serving as a brake is actuated frictionally to engage the carriermember and thereby restrain it against rotation so that power applied tothe sun gear will turn the ring gear in the opposite direction. Thus, ifthe ring gear is operatively connected to the drive wheels of a vehicle,such an arrangement is capable of reversing the rotational direction ofthe drive wheels, and thereby reversing the direction of the vehicleitself.

In a simple set of planetary gears, if any two rotational speeds of thesun gear, the planet carrier member, and the ring gear are known, thenthe speed of the third member can be determined using a simple rule. Therotational speed of the carrier member is always proportional to thespeeds of the sun and the ring, weighted by their respective numbers ofteeth. For example, a ring gear may have twice as many teeth as the sungear in the same set. The speed of the carrier member is then the sum oftwo-thirds the speed of the ring gear and one-third the speed of the sungear. If one of these three members rotates in an opposite direction,the arithmetic sign is negative for the speed of that member inmathematical calculations.

The torque on the sun gear, the carrier member, and the ring gear canalso be simply related to one another if this is done withoutconsideration of the masses of the gears, the acceleration of the gears,or friction within the gear set, all of which have a relatively minorinfluence in a well designed transmission. The torque applied to the sungear of a simple planetary gear set must balance the torque applied tothe ring gear, in proportion to the number of teeth on each of thesegears. For example, the torque applied to a ring gear with twice as manyteeth as the sun gear in that set must be twice that applied to the sungear, and must be applied in the same direction. The torque applied tothe carrier member must be equal in magnitude and opposite in directionto the sum of the torque on the sun gear and the torque on the ringgear.

In a compound planetary gear set, the utilization of inner and outersets of planet gears effects an exchange in the roles of the ring gearand the planet carrier member in comparison to a simple planetary gearset. For instance, if the sun gear is held stationary, the planetcarrier member will rotate in the same direction as the ring gear, butthe planet carrier member with inner and outer sets of planet gears willtravel faster than the ring gear, rather than slower.

In a compound planetary gear set having meshing inner and outer sets ofplanet gears the speed of the ring gear is proportional to the speeds ofthe sun gear and the planet carrier member, weighted by the number ofteeth on the sun gear and the number of teeth filled by the planetgears, respectively. For example, the difference between the ring andthe sun filled by the planet gears might be as many teeth as are on thesun gear in the same set. In that situation the speed of the ring gearwould be the sum of two-thirds the speed of the carrier member and onethird the speed of the sun. If the sun gear or the planet carrier memberrotates in an opposite direction, the arithmetic sign is negative forthat speed in mathematical calculations.

If the sun gear were to be held stationary, then a carrier member withinner and outer sets of planet gears will turn in the same direction asthe rotating ring gear of that set. On the other hand, if the sun gearwere to be held stationary and the carrier member were to be driven,then planet gears in the inner set that engage the sun gear roll, or“walk,” along the sun gear, turning in the same direction that thecarrier member is rotating. Pinion gears in the outer set that mesh withpinion gears in the inner set will turn in the opposite direction, thusforcing a meshing ring gear in the opposite direction, but only withrespect to the planet gears with which the ring gear is meshinglyengaged. The planet gears in the outer set are being carried along inthe direction of the carrier member. The effect of the rotation of thepinion gears in the outer set on their own axis and the greater effectof the orbital motion of the planet gears in the outer set due to themotion of the carrier member are combined, so the ring rotates in thesame direction as the carrier member, but not as fast as the carriermember.

If the carrier member in such a compound planetary gear set were to beheld stationary and the sun gear were to be rotated, then the ring gearwill rotate with less speed and in the same direction as the sun gear.If the ring gear of a simple planetary gear set is held stationary andthe sun gear is rotated, then the carrier member supporting a single setof planet gears will rotate with less speed and in the same direction asthe sun gear. Thus, one can readily observe the exchange in rolesbetween the carrier member and the ring gear that is caused by the useof inner and outer sets of planet gears which mesh with one another, incomparison with the usage of a single set of planet gears in a simpleplanetary gear set.

The normal action of an electrically variable transmission is totransmit mechanical power from the input to the output. As part of thistransmission action, one of its two motor/generators acts as a generatorof electrical power. The other motor/generator acts as a motor and usesthat electrical power. As the speed of the output increases from zero toa high speed, the two motor/generators 80, 82 gradually exchange rolesas generator and motor, and may do so more than once. These exchangestake place around mechanical points, where essentially all of the powerfrom input to output is transmitted mechanically and no substantialpower is transmitted electrically.

In a hybrid electrically variable transmission system, the battery 86may also supply power to the transmission or the transmission may supplypower to the battery. If the battery is supplying substantial electricpower to the transmission, such as for vehicle acceleration, then bothmotor/generators may act as motors. If the transmission is supplyingelectric power to the battery, such as for regenerative braking, bothmotor/generators may act as generators. Very near the mechanical pointsof operation, both motor/generators may also act as generators withsmall electrical power outputs, because of the electrical losses in thesystem.

Contrary to the normal action of the transmission, the transmission mayactually be used to transmit mechanical power from the output to theinput. This may be done in a vehicle to supplement the vehicle brakesand to enhance or to supplement regenerative braking of the vehicle,especially on long downward grades. If the power flow through thetransmission is reversed in this way, the roles of the motor/generatorswill then be reversed from those in normal action.

Specific Operating Considerations

Each of the embodiments described herein has fourteen to sixteenfunctional requirements (corresponding with the 14 to 16 rows of eachoperating mode table shown in the Figures) which may be grouped intofive operating modes. These five operating modes are described below andmay be best understood by referring to the respective operating modetable accompanying each transmission stick diagram, such as theoperating mode tables of FIG. 1 b, 2 b, 3 b, etc.

The first operating mode is the “battery reverse mode” which correspondswith the first row (Batt Rev) of each operating mode table, such as thatof FIG. 1 b. In this mode, the engine is off and the transmissionelement connected to the engine is not controlled by engine torque,though there may be some residual torque due to the rotational inertiaof the engine. The EVT is driven by one of the motor/generators usingenergy from the battery, causing the vehicle to move in reverse.Depending on the kinematic configuration, the other motor/generator mayor may not rotate in this mode, and may or may not transmit torque. Ifit does rotate, it is used to generate energy which is stored in thebattery. In the embodiment of FIG. 1 b, in the battery reverse mode, thegenerator 80 has a torque of −1.50, the motor 82 has a torque of −1.00,and a torque ratio of −2.25 is achieved, by way of example. In eachoperating mode table an (M) next to a torque value in themotor/generator columns 80 and 82 indicates that the motor/generator isacting as a motor, and the absence of an (M) indicates that themotor/generator is acting as generator.

The second operating mode is the “EVT reverse mode” (or mechanicalreverse mode) which corresponds with the second row (EVT Rev) of eachoperating mode table, such as that of FIG. 1 b. In this mode, the EVT isdriven by the engine and by one of the motor/generators. The othermotor/generator operates in generator mode and transfers 100% of thegenerated energy back to the driving motor. The net effect is to drivethe vehicle in reverse. Referring to FIG. 1 b, for example, in the EVTreverse mode, the clutch 50 is engaged, the generator 80 has a torque of−1.32 units, the motor 82 has a torque of −1.97 units, and an outputtorque of −8.33 is achieved, corresponding to an engine torque of 1unit.

The third operating mode includes the “reverse and forward launch modes”(also referred to as “torque converter reverse and forward modes”)corresponding with the third and fourth rows (TC Rev and TC For) of eachoperating mode table, such as that of FIG. 1 b. In this mode, the EVT isdriven by the engine and one of the motor/generators. A selectablefraction of the energy generated in the generator unit is stored in thebattery, with the remaining energy being transferred to the motor. InFIG. 1, this fraction is approximately 99%. The ratio of transmissionoutput speed to engine speed (transmission speed ratio) is approximately±0.001 (the positive sign indicates that the vehicle is creeping forwardand negative sign indicates that the vehicle is creeping backwards).Referring to FIG. 1 b, in the TC Reverse mode, the clutch 50 is engaged,the motor/generator 80 acts as a generator with −1.18 units of torque,the motor/generator 82 acts as a motor with −1.68 units of torque, and atorque ratio of −7.00 is achieved. In the TC Forward mode, the clutch 50is engaged, the motor/generator 80 acts as a motor with 0.11 units oftorque, the motor/generator 82 acts as a generator with 0.89 units oftorque, and a torque ratio of 4.69 is achieved.

The fourth operating mode is a “continuously variable transmission rangemode” which includes the Range 1.1, Range 1.2, Range 1.3, Range 1.4,Range 1.5, Range 1.6, Range 1.7 and Range 1.8 operating pointscorresponding with rows 5-12 of each operating point table, such as thatof FIG. 1 b. In this mode, the EVT is driven by the engine as well asone of the motor/generators operating as a motor. The othermotor/generator operates as a generator and transfers 100% of thegenerated energy back to the motor. The operating points represented byRange 1.1, 1.2, . . . , etc. are discrete points in the continuum offorward speed ratios provided by the EVT. For example in FIG. 1 b, arange of torque ratios from 4.69 to 0.54 is achieved with the clutch 50engaged.

The fifth operating mode includes the “fixed ratio” modes (F1, F2, F3and F4) corresponding with rows 13-16 of each operating mode table (i.e.operating mode table), such as that of FIG. 1 b. In this mode thetransmission operates like a conventional automatic transmission, withtwo torque transmitting devices engaged to create a discretetransmission ratio. The clutching table accompanying each figure showsonly four fixed-ratio forward speeds but additional fixed ratios may beavailable. Referring to FIG. 1 b, in fixed ratio F1 the clutch 50 andbrake 57 are engaged to achieve a fixed torque ratio of 3.71. In fixedratio F2, the clutches 50 and 52 are engaged to achieve a fixed ratio of1.68. In fixed ratio F3, the clutches 50 and 54 are engaged to achieve afixed ratio of 1.00. In fixed ratio F4, the clutch 50 and brake 55 areengaged to achieve a fixed ratio of 0.67. Accordingly, each “X” in thecolumn of motor/generators 80 or 82, respectively, in FIG. 1 b indicatesthat the brake 55 or 57, respectively, is engaged and themotor/generator 80, 82 is not rotating.

The powertrain 10 may also operate in a “charge-depleting mode”. Forpurposes of the present invention, a “charge-depleting mode” is a modewherein the vehicle is powered primarily by an electric motor/generatorsuch that the battery 86 is depleted or nearly depleted when the vehiclereaches its destination. In other words, during the charge-depletingmode, the engine 12 is only operated to the extent necessary to ensurethat the battery 86 is not depleted before the destination is reached. Aconventional hybrid vehicle operates in a “charge-sustaining mode”,wherein if the battery charge level drops below a predetermined level(e.g., 25%) the engine is automatically run to recharge the battery.Therefore, by operating in a charge-depleting mode, the hybrid vehiclecan conserve some or all of the fuel that would otherwise be expended tomaintain the 25% battery charge level in a conventional hybrid vehicle.It should be appreciated that the vehicle powertrain is preferably onlyoperated in the charge-depleting mode if the battery 86 can be rechargedafter the destination is reached by plugging it into an energy source(not shown).

Also, the engine 12 may be powered using various types of fuel toimprove the efficiency and fuel economy of a particular application.Such fuels may include, for example, gasoline; diesel; ethanol; dimethylether; etc.

The transmission 14 is capable of operating in so-called single or dualmodes. In single mode, the engaged torque transmitting device remainsthe same for the entire continuum of forward speed ratios (representedby the discrete points: Ranges 1.1, 1.2, 1.3 and 1.4). In dual mode, theengaged torque transmitting device is switched at some intermediatespeed ratio (e.g., Range 2.1 in FIG. 2). Depending on the mechanicalconfiguration, this change in torque transmitting device engagement hasadvantages in reducing element speeds in the transmission.

As set forth above, the engagement schedule for the torque transmittingdevices is shown in the operating mode table and fixed ratio mode tableof FIG. 1 b. FIG. 1 b also provides an example of torque ratios that areavailable utilizing the ring gear/sun gear tooth ratios given by way ofexample in FIG. 1 b. The N_(R1)/N_(S1) value is the tooth ratio of theplanetary gear set 20; the N_(R2)/N_(S2) value is the tooth ratio of theplanetary gear set 30; and the N_(R3)/N_(S3) value is the tooth ratio ofthe planetary gear set 40. Also, the chart of FIG. 1 b describes theratio steps that are attained utilizing the sample of tooth ratiosgiven. For example, the step ratio between first and second fixedforward torque ratios is 2.21, the step ratio between the second andthird fixed forward torque ratios is 1.68, the step ratio between thethird and fourth fixed forward torque ratios is 1.49, and the ratiospread is 5.54.

Description of a Second Exemplary Embodiment

With reference to FIG. 2 a, a powertrain 110 is shown, including anengine 12 connected to another embodiment of the improved electricallyvariable transmission, designated generally by the numeral 114.Transmission 114 is designed to receive at least a portion of itsdriving power from the engine 12.

In the embodiment depicted the engine 12 may also be a fossil fuelengine, such as a diesel engine which is readily adapted to provide itsavailable power output typically delivered at a constant number ofrevolutions per minute (RPM). As shown, the engine 12 has an outputshaft that serves as the input member 17 of the transmission 14. Atransient torque damper (not shown) may also be implemented between theengine 12 and the input member 17 of the transmission.

Irrespective of the means by which the engine 12 is connected to thetransmission input member 17, the transmission input member 17 isoperatively connected to a planetary gear set in the transmission 114.An output member 19 of the transmission 114 is connected to a finaldrive 16.

The transmission 114 utilizes three differential gear sets, preferablyin the nature of planetary gear sets 120, 130 and 140. The planetarygear set 120 employs an outer gear member 124, typically designated asthe ring gear. The ring gear member 124 circumscribes an inner gearmember 122, typically designated as the sun gear. A carrier member 126rotatably supports a plurality of planet gears 127 such that each planetgear 127 meshingly engages both the outer, ring gear member 124 and theinner, sun gear member 122 of the first planetary gear set 120.

The planetary gear set 130 also has an outer gear member 134, often alsodesignated as the ring gear, that circumscribes an inner gear member132, also often designated as the sun gear. A plurality of planet gears137 are also rotatably mounted in a carrier member 136 such that eachplanet gear member 137 simultaneously, and meshingly, engages both theouter, ring gear member 134 and the inner, sun gear member 132 of theplanetary gear set 130.

The planetary gear set 140 also has an outer gear member 144, often alsodesignated as the ring gear, that circumscribes an inner gear member142, also often designated as the sun gear. A plurality of planet gears147 are also rotatably mounted in a carrier member 146 such that eachplanet gear member 147 simultaneously, and meshingly, engages both theouter, ring gear member 144 and the inner, sun gear member 142 of theplanetary gear set 140.

The transmission output member 19 is connected with the carrier member126 of the planetary gear set 120. A first interconnecting member 170continuously connects the carrier member 126 of the planetary gear set120 with the ring gear member 134 of the planetary gear set 130. Asecond interconnecting member 172 continuously connects the sun gearmember 122 of the planetary gear set 120 with the carrier member 146 ofthe planetary gear set 140. A third interconnecting member 174continuously connects the sun gear member 132 of the planetary gear set130 with the sun gear member 142 of the planetary gear set 140. A fourthinterconnecting member 176 continuously connects the ring gear member124 of the planetary gear set 120 with the transmission housing 160.

The transmission 114 also incorporates first and second motor/generators180 and 182, respectively. The stator of the first motor/generator 180is secured to the transmission housing 160. The rotor of the firstmotor/generator 180 is secured to the sun gear member 142 of theplanetary gear set 140.

The stator of the second motor/generator 182 is also secured to thetransmission housing 160. The rotor of the second motor/generator 182 isselectively connectable to ring gear member 144 of the planetary gearset 140 or the carrier member 146 of the planetary gear set 140 viaclutches A and B, respectively. Within the scope of the invention, box192, shown in phantom, may be a dog clutch represented by clutches orswitches A and B. A dog clutch could be utilized to accomplish theselective engagement as achieved by clutches A and B, as is understoodby those skilled in the art.

A first torque transmitting device, such as input clutch 150,selectively connects the carrier member 136 of the planetary gear set130 with the input member 17. A second torque transmitting device, suchas clutch 152, selectively connects the sun gear member 142 of theplanetary gear set 140 with the carrier member 146 of the planetary gearset 140. A third torque transmitting device, such as clutch 154,selectively connects the carrier member 136 of the planetary gear set130 with the ring gear member 134 of the planetary gear set 130. Afourth torque transmitting device, such as the brake 155, is connectedin parallel with the motor/generator 180 for selectively brakingrotation thereof. A fifth torque transmitting device, such as the brake157, is connected in parallel with the motor/generator 182 forselectively braking rotation thereof. The first, second, third, fourthand fifth torque transmitting devices 150, 152, 154, 155 and 157 areemployed to assist in the selection of the operational modes of thehybrid transmission 114.

Returning now to the description of the power sources, it should beapparent from the foregoing description, and with particular referenceto FIG. 2 a, that the transmission 114 selectively receives power fromthe engine 12. The hybrid transmission also exchanges power with anelectric power source 186, which is operably connected to a controller188. The electric power source 186 may be one or more batteries. Otherelectric power sources, such as fuel cells, that have the ability toprovide, or store, and dispense electric power may be used in place ofbatteries without altering the concepts of the present invention.

As described previously, each embodiment has fifteen or sixteenfunctional requirements (corresponding with the 15 or 16 rows of eachoperating mode table shown in the Figures) which may be grouped intofive operating modes. The first operating mode is the “battery reversemode” which corresponds with the first row (Batt Rev) of the operatingmode table of FIG. 2 b. In this mode, the engine is off and thetransmission element connected to the engine is effectively allowed tofreewheel, subject to engine inertia torque. The EVT is driven by one ofthe motor/generators using energy from the battery, causing the vehicleto move in reverse. The other motor/generator may or may not rotate inthis mode. As shown in FIG. 2 b, in this mode clutch A is engaged, thegenerator 180 has a torque of −1.50 units, the motor 182 has a torque of−1.00 units and an output torque of −2.25 is achieved, by way ofexample.

The second operating mode is the “EVT reverse mode” (or mechanicalreverse mode) which corresponds with the second row (EVT Rev) of theoperating mode table of FIG. 2 b. In this mode, the EVT is driven by theengine and by one of the motor/generators. The other motor/generatoroperates in generator mode and transfers 100% of the generated energyback to the driving motor. The net effect is to drive the vehicle inreverse. In this mode, the clutches 150 and A are engaged, the generator180 has a torque of −1.32 units, the motor 182 has a torque of −1.97units, and an output torque of −8.33 is achieved, corresponding to aninput torque of 1 unit.

The third operating mode includes the “reverse and forward launch modes”corresponding with the third and fourth rows (TC Rev and TC For) of eachoperating mode table, such as that of FIG. 2 b. In this mode, the EVT isdriven by the engine and one of the motor/generators. A selectablefraction of the energy generated in the generator unit is stored in thebattery, with the remaining energy being transferred to the motor. In TCRev, the clutches 150 and A are engaged, the motor/generator 180 acts asa generator with −1.18 units of torque, the motor/generator 182 acts asa motor with −1.68 units of torque, and a torque ratio of −7.00 isachieved. In TC For, the clutches 150 and A are engaged, themotor/generator 180 acts as a motor with 0.11 units of torque, themotor/generator 182 acts as a generator with 0.89 units of torque, and atorque ratio of 4.69 is achieved. For these torque ratios, approximately99% of the generator energy is stored in the battery.

The fourth operating mode includes the “Range 1.1, Range 1.2, Range 1.3,Range 1.4, Range 2.1, Range 2.2, Range 2.3 and Range 2.4” modescorresponding with rows 5-12 of the operating mode table of FIG. 2 b. Inthis mode, the EVT is driven by the engine as well as one of themotor/generators operating as a motor. The other motor/generatoroperates as a generator and transfers 100% of the generated energy backto the motor. The operating points represented by Range 1.1, 1.2 . . . ,etc. are discrete points in the continuum of forward speed ratiosprovided by the EVT. For example in FIG. 2 b, a range of ratios from4.69 to 1.86 is achieved with the clutches 150 and A engaged, and arange of ratios from 1.36 to 0.54 is achieved with the clutches 150 andB engaged.

The fifth operating mode includes the fixed “ratio” modes (F1, F2, F3and F4) corresponding with rows 13-16 of the operating mode table ofFIG. 2 b. In this mode the transmission operates like a conventionalautomatic transmission, with one torque transmitting device engaged tocreate a discrete transmission ratio. In fixed ratio F1 the clutches150, A and brake 157 are engaged to achieve a fixed ratio of 3.71. Infixed ratio F2, the clutches 150, 152 and A are engaged to achieve afixed ratio of 1.68. In fixed ratio F3, the clutches 150, 154 and A areengaged to achieve a fixed ratio of 1.00. In fixed ratio F4, theclutches 150, A and brake 155 are engaged to achieve a fixed ratio of0.67.

As set forth above, the engagement schedule for the torque transmittingdevices is shown in the operating mode table and fixed ratio mode tableof FIG. 2 b. FIG. 2 b also provides an example of torque ratios that areavailable utilizing the ring gear/sun gear tooth ratios given by way ofexample in FIG. 2 b. The N_(R1)/N_(S1) value is the tooth ratio of theplanetary gear set 120; the N_(R2)/N_(S2) value is the tooth ratio ofthe planetary gear set 130; and the N_(R3)/N_(S3) value is the toothratio of the planetary gear set 140. Also, the chart of FIG. 2 bdescribes the ratio steps that are attained utilizing the sample oftooth ratios given. For example, the step ratio between first and secondfixed forward torque ratios is 2.21, and the ratio spread is 5.54.

Description of a Third Exemplary Embodiment

With reference to FIG. 3 a, a powertrain 210 is shown, including anengine 12 connected to another embodiment of the improved electricallyvariable transmission, designated generally by the numeral 214. Thetransmission 214 is designed to receive at least a portion of itsdriving power from the engine 12. As shown, the engine 12 has an outputshaft that serves as the input member 17 of the transmission 214. Atransient torque damper (not shown) may also be implemented between theengine 12 and the input member 17 of the transmission 214.

Irrespective of the means by which the engine 12 is connected to thetransmission input member 17, the transmission input member isoperatively connected to a planetary gear set in the transmission 214.An output member 19 of the transmission 214 is connected to a finaldrive 16.

The transmission 214 utilizes three differential gear sets, preferablyin the nature of planetary gear sets 220, 230 and 240. The planetarygear set 220 employs an outer gear member 224, typically designated asthe ring gear. The ring gear member 224 circumscribes an inner gearmember 222, typically designated as the sun gear. A carrier member 226rotatably supports a plurality of planet gears 227 such that each planetgear 227 meshingly engages both the outer, ring gear member 224 and theinner, sun gear member 222 of the first planetary gear set 220.

The planetary gear set 230 also has an outer ring gear member 234 thatcircumscribes an inner sun gear member 232. A plurality of planet gears237 are also rotatably mounted in a carrier member 236 such that eachplanet gear 237 simultaneously, and meshingly, engages both the outerring gear member 234 and the inner sun gear member 232 of the planetarygear set 230.

The planetary gear set 240 also has an outer ring gear member 244 thatcircumscribes an inner sun gear member 242. A plurality of planet gears247 are rotatably mounted in a carrier member 246 such that each planetgear member 247 simultaneously and meshingly engages both the outer,ring gear member 244 and the inner, sun gear member 242 of the planetarygear set 240.

The transmission output member 19 is connected to the carrier member246. A first interconnecting member 270 continuously connects the sungear member 222 with the sun gear member 232. A second interconnectingmember 272 continuously connects the carrier member 226 with the ringgear member 244. A third interconnecting member 274 continuouslyconnects the ring gear member 234 with the carrier member 246. A fourthinterconnecting member 276 continuously connects the ring gear member224 with the transmission housing 260.

The transmission 214 also incorporates first and second motor/generators280 and 282, respectively. The stator of the first motor/generator 280is secured to the transmission housing 260. The rotor of the firstmotor/generator 280 is secured to the sun gear member 222. The stator ofthe second motor/generator 282 is also secured to the transmissionhousing 260. The rotor of the second motor/generator 282 is secured tothe sun gear member 242.

A first torque transmitting device, such as input clutch 250,selectively connects carrier member 236 with the input member 17. Asecond torque transmitting device, such as clutch 252, selectivelyconnects the carrier member 246 with the sun gear member 242. A thirdtorque transmitting device, such as clutch 254, selectively connects thecarrier member 226 with the ring gear member 234. A fourth torquetransmitting device, such as the brake 255, is connected in parallelwith the motor/generator 280 for selectively braking rotation thereof. Afifth torque transmitting device, such as brake 257, is connected inparallel with the motor/generator 282 for selectively braking rotationthereof. The first, second, third, fourth and fifth torque transmittingdevices 250, 252, 254, 255 and 257 are employed to assist in theselection of the operational modes of the hybrid transmission 214.

The hybrid transmission 214 receives power from the engine 12, and alsofrom electric power source 286, which is operably connected to acontroller 288.

The operating mode table of FIG. 3 b illustrates the clutchingengagements, motor/generator conditions and output/input ratios for thefive operating modes of the transmission 214. These modes include the“battery reverse mode” (Batt Rev), “EVT reverse mode” (EVT Rev),“reverse and forward launch modes” (TC Rev and TC For), “range 1.1, 1.2,1.3 . . . modes” and “fixed ratio modes” (F1, F2, F3 and F4) asdescribed previously.

As set forth above the engagement schedule for the torque transmittingdevices is shown in the operating mode table and fixed ratio mode tableof FIG. 3 b. FIG. 3 b also provides an example of torque ratios that areavailable utilizing the ring gear/sun gear tooth ratios given by way ofexample in FIG. 3 b. The N_(R1)/N_(S1) value is the tooth ratio of theplanetary gear set 220; the N_(R2)/N_(S2) value is the tooth ratio ofthe planetary gear set 230; and the N_(R3)/N_(S3) value is the toothratio of the planetary gear set 240. Also, the chart of FIG. 3 bdescribes the ratio steps that are attained utilizing the sample oftooth ratios given. For example, the step ratio between the first andsecond fixed forward torque ratios is 1.28, and the ratio spread is3.62.

Description of a Fourth Exemplary Embodiment

With reference to FIG. 4 a, a powertrain 310 is shown, including anengine 12 connected to another embodiment of the improved electricallyvariable transmission, designated generally by the numeral 314. Thetransmission 314 is designed to receive at least a portion of itsdriving power from the engine 12.

As shown, the engine 12 has an output shaft that serves as the inputmember 17 of the transmission 314. A transient torque damper (not shown)may also be implemented between the engine 12 and the input member 17 ofthe transmission.

Irrespective of the means by which the engine 12 is connected to thetransmission input member 17, the transmission input member 17 isoperatively connected to a planetary gear set in the transmission 314.An output member 19 of the transmission 314 is connected to a finaldrive 16.

The transmission 314 utilizes three planetary gear sets 320, 330 and340. The planetary gear set 320 employs an outer ring gear member 324which circumscribes an inner sun gear member 322. A carrier member 326rotatably supports a plurality of planet gears 327 such that each planetgear 327 meshingly engages both the outer ring gear member 324 and theinner sun gear member 322 of the first planetary gear set 320.

The planetary gear set 330 also has an outer ring gear member 334 thatcircumscribes an inner sun gear member 332. A plurality of planet gears337 are also rotatably mounted in a carrier member 336 such that eachplanet gear member 337 simultaneously, and meshingly engages both theouter, ring gear member 334 and the inner, sun gear member 332 of theplanetary gear set 330.

The planetary gear set 340 also has an outer ring gear member 344 thatcircumscribes an inner sun gear member 342. A plurality of planet gears347 are also rotatably mounted in a carrier member 346 such that eachplanet gear member 347 simultaneously, and meshingly, engages both theouter ring gear member 344 and the inner sun gear member 342 of theplanetary gear set 340.

The transmission output member 19 is connected with the carrier member336. A first interconnecting member 370 continuously connects the sungear member 322 with the sun gear member 332. A second interconnectingmember 372 continuously connects the carrier member 326 with the carriermember 346. A third interconnecting member 374 continuously connects thering gear member 334 with the sun gear member 342. A fourthinterconnecting member 376 continuously connects the sun gear member 322with the transmission housing 360.

The transmission 314 also incorporates first and second motor/generators380 and 382, respectively. The stator of the first motor/generator 380is secured to the transmission housing 360. The rotor of the firstmotor/generator 380 is secured to the sun gear member 342. The stator ofthe second motor/generator 382 is also secured to the transmissionhousing 360. The rotor of the second motor/generator 382 is secured tothe ring gear member 344.

A first torque transmitting device, such as input clutch 350,selectively connects the ring gear member 324 with the input member. Asecond torque transmitting device, such as input clutch 352, selectivelyconnects the carrier member 326, and the carrier member 346 viainterconnecting member 372, with the input member 17. A third torquetransmitting device, such as clutch 354, selectively connects thecarrier member 326 with the ring gear member 334. A fourth torquetransmitting device, such as the brake 355, is connected in parallelwith the motor/generator 382 for selectively braking rotation thereof.The first, second, third and fourth torque transmitting devices 350,352, 354 and 355 are employed to assist in the selection of theoperational modes of the transmission 314.

The hybrid transmission 314 receives power from the engine 12, and alsoexchanges power with an electric power source 386, which is operablyconnected to a controller 388.

The operating mode table of FIG. 4 b illustrates the clutchingengagements, motor/generator conditions and output/input ratios for thefive operating modes of the transmission 314. These modes include the“battery reverse mode” (Batt Rev), the “EVT reverse mode” (EVT Rev),“reverse and forward launch modes” (TC Rev and TC For), “continuouslyvariable transmission range modes” (Range 1.1, 1.2, 1.3 . . . ) and“fixed ratio modes” (F1, F2, F3) as described previously.

As set forth above, the engagement schedule for the torque transmittingdevices is shown in the operating mode table and fixed ratio mode tableof FIG. 4 b. FIG. 4 b also provides an example of torque ratios that areavailable utilizing the ring gear/sun gear tooth ratios given by way ofexample in FIG. 4 b. The N_(R1)/N_(S1) value is the tooth ratio of theplanetary gear set 320; the N_(R2)/N_(S2) value is the tooth ratio ofthe planetary gear set 330; and the N_(R3)/N_(S3) value is the toothratio of the planetary gear set 340. Also, the chart of FIG. 4 bdescribes the ratio steps that are attained utilizing the sample oftooth ratios given. For example, the step ratio between first and secondfixed forward torque ratios is 1.44, and the ratio spread is 3.01.

Description of a Fifth Exemplary Embodiment

With reference to FIG. 5 a, a powertrain 410 is shown, including anengine 12 connected to another embodiment of the improved electricallyvariable transmission, designated generally by the numeral 414. Thetransmission 414 is designed to receive at least a portion of itsdriving power from the engine 12.

As shown, the engine 12 has an output shaft that serves as the inputmember 17 of the transmission 414. A transient torque damper (not shown)may also be implemented between the engine 12 and the input member 17 ofthe transmission.

Irrespective of the means by which the engine 12 is connected to thetransmission input member 17, the transmission input member 17 isoperatively connected to a planetary gear set in the transmission 414.An output member 19 of the transmission 414 is connected to a finaldrive 16.

The transmission 414 utilizes three planetary gear sets 420, 430 and440. The planetary gear set 420 employs an outer ring gear member 424which circumscribes an inner sun gear member 422. A carrier member 426rotatably supports a plurality of planet gears 427 such that each planetgear 427 meshingly engages both the outer ring gear member 424 and theinner sun gear member 422 of the first planetary gear set 420.

The planetary gear set 430 also has an outer ring gear member 434 thatcircumscribes an inner sun gear member 432. A plurality of planet gears437 are also rotatably mounted in a carrier member 436 such that eachplanet gear member 437 simultaneously, and meshingly engages both theouter, ring gear member 434 and the inner, sun gear member 432 of theplanetary gear set 430.

The planetary gear set 440 also has an outer ring gear member 444 thatcircumscribes an inner sun gear member 442. A plurality of planet gears447, 448 are also rotatably mounted in a carrier member 446 such thateach planet gear member 447 engages inner sun gear member 442 and theplanet gear members 448 simultaneously, and meshingly, both the outerring gear member 444 and the respective planet gear 447 of the planetarygear set 440.

The transmission output member 19 is continuously connected with thecarrier member 436. A first interconnecting member 470 continuouslyconnects the sun gear member 422 with the sun gear member 432. A secondinterconnecting member 472 continuously connects the carrier member 426with the ring gear member 444. A third interconnecting member 474continuously connects the ring gear member 434 with the sun gear member442. A fourth interconnecting member 476 continuously connects the sungear member 422 with the transmission housing 460.

The transmission 414 also incorporates first and second motor/generators480 and 482, respectively. The stator of the first motor/generator 480is secured to the transmission housing 460. The rotor of the firstmotor/generator 480 is secured to the sun gear member 442. The stator ofthe second motor/generator 482 is also secured to the transmissionhousing 460. The rotor of the second motor/generator 482 is secured tothe carrier member 446.

A first torque transmitting device, such as input clutch 450,selectively connects the ring gear member 424 with the input member 17.A second torque transmitting device, such as clutch 452, selectivelyconnects the carrier member 426, and the ring gear member 444 via theinterconnecting member 472, with the input member 17. A third torquetransmitting device, such as clutch 454, selectively connects thecarrier member 426 with the ring gear member 434. A fourth torquetransmitting device, such as the brake 455, is connected in parallelwith the motor/generator 482 for selectively braking rotation thereof.The first, second, third and fourth torque transmitting devices 450,452, 454 and 455 are employed to assist in the selection of theoperational modes of the transmission 414. The hybrid transmission 414receives power from the engine 12 and also from an electric power source486, which is operably connected to a controller 488.

The operating mode table of FIG. 5 b illustrates the clutchingengagements, motor/generator conditions and output/input ratios for thefive operating modes of the transmission 414. These modes include the“battery reverse mode” (Batt Rev), the “EVT reverse mode” (EVT Rev),“reverse and forward launch modes” (TC Rev and TC For), “continuouslyvariable transmission range modes” (Range 1.1, 1.2, 1.3 . . . ) and“fixed ratio modes” (F1, F2 and F3) as described previously.

As set forth above, the engagement schedule for the torque transmittingdevices is shown in the operating mode table and fixed ratio mode tableof FIG. 5 b. FIG. 5 b also provides an example of torque ratios that areavailable utilizing the ring gear/sun gear tooth ratios given by way ofexample in FIG. 5 b. The N_(R1)/N_(S1) value is the tooth ratio of theplanetary gear set 420; the N_(R2)/N_(S2) value is the tooth ratio ofthe planetary gear set 430; and the N_(R3)/N_(S3) value is the toothratio of the planetary gear set 440. Also, the chart of FIG. 5 bdescribes the ratio steps that are attained utilizing the sample oftooth ratios given. For example, the step ratio between first and secondfixed forward torque ratios is 1.44, and the ratio spread is 3.01.

Description of a Sixth Exemplary Embodiment

With reference to FIG. 6 a, a powertrain 510 is shown, including anengine 12 connected to another embodiment of the improved electricallyvariable transmission, designated generally by the numeral 514. Thetransmission 514 is designed to receive at least a portion of itsdriving power from the engine 12.

As shown, the engine 12 has an output shaft that serves as the inputmember 17 of the transmission 514. A transient torque damper (not shown)may also be implemented between the engine 12 and the input member 17 ofthe transmission.

Irrespective of the means by which the engine 12 is connected to thetransmission input member 17, the transmission input member 17 isoperatively connected to a planetary gear set in the transmission 514.An output member 19 of the transmission 514 is connected to a finaldrive 16.

The transmission 514 utilizes three planetary gear sets 520, 530 and540. The planetary gear set 520 employs an outer ring gear member 524which circumscribes an inner sun gear member 522. A carrier member 526rotatably supports a plurality of planet gears 527 such that each planetgear 527 meshingly engages both the outer ring gear member 524 and theinner sun gear member 522 of the first planetary gear set 520.

The planetary gear set 530 also has an outer ring gear member 534 thatcircumscribes an inner sun gear member 532. A plurality of planet gears537 are also rotatably mounted in a carrier member 536 such that eachplanet gear member 537 simultaneously, and meshingly engages both theouter, ring gear member 534 and the inner, sun gear member 532 of theplanetary gear set 530.

The planetary gear set 540 also has an outer ring gear member 544 thatcircumscribes an inner sun gear member 542. A plurality of planet gears547 are also rotatably mounted in a carrier member 546 such that eachplanet gear member 547 simultaneously, and meshingly engages both theinner, sun gear member 542 and the outer, ring gear member 544 of theplanetary gear set 540.

The transmission output member 19 is continuously connected with thecarrier member 536. The first interconnecting member 570 continuouslyconnects the sun gear member 522 with the sun gear member 532. A secondinterconnecting member 572 continuously connects the carrier member 526with the carrier member 546. A third interconnecting member 574continuously connects the ring gear member 534 with the sun gear member542. A fourth interconnecting member 576 continuously connects the sungear member 522 with the transmission housing 560.

The transmission 514 also incorporates first and second motor/generators580 and 582, respectively. The stator of the first motor/generator 580is secured to the transmission housing 560. The rotor of the firstmotor/generator 580 is secured to the sun gear member 542. The stator ofthe second motor/generator 582 is also secured to the transmissionhousing 560. The rotor of the second motor/generator 582 is secured tothe ring gear member 544.

A first torque transmitting device, such as input clutch 550,selectively connects the ring gear member 524 with the input member 17.A second torque transmitting device, such as input clutch 552,selectively connects the ring gear member 544 with the input member 17.A third torque transmitting device, such as brake 554, selectivelyconnects the carrier member 546 with the transmission housing 560. Afourth torque transfer device, such as the brake 555, is connected inparallel with the motor/generator 582 for selectively braking rotationthereof. The first, second, third and fourth torque transmitting devices550, 552, 554 and 555 are employed to assist in the selection of theoperational modes of the hybrid transmission 514.

The hybrid transmission 514 receives power from the engine 12, and alsoexchanges power with an electric power source 586, which is operablyconnected to a controller 588.

The operating mode table of FIG. 6 b illustrates the clutchingengagements, motor/generator conditions and output/input ratios for thefive operating modes of the transmission 514. These modes include the“battery reverse mode” (Batt Rev), the “EVT reverse mode” (EVT Rev),“reverse and forward launch modes” (TC Rev and TC For), “continuouslyvariable transmission range modes” (Range 1.1, 1.2, 1.3 . . . ) and“fixed ratio modes” (R1, F1, F2) as described previously.

As set forth above, the engagement schedule for the torque transmittingdevices is shown in the operating mode table and fixed ratio mode tableof FIG. 6 b. FIG. 6 b also provides an example of torque ratios that areavailable utilizing the ring gear/sun gear tooth ratios given by way ofexample in FIG. 6 b. The N_(R1)/N_(S1) value is the tooth ratio of theplanetary gear set 520; the N_(R2)/N_(S2) value is the tooth ratio ofthe planetary gear set 530; and the N_(R3)/N_(S3) value is the toothratio of the planetary gear set 540. Also, the chart of FIG. 6 bdescribes the ratio steps that are attained utilizing the sample oftooth ratios given. For example, the step ratio between first and secondfixed forward torque ratios is 3.01.

In the claims, the language “continuously connected” or “continuouslyconnecting” refers to a direct connection or a proportionally gearedconnection, such as gearing to an offset axis. Also, the “stationarymember” or “ground” may include the transmission housing (case) or anyother non-rotating component or components. Also, when a torquetransmitting mechanism is said to connect something to a member of agear set, it may also be connected to an interconnecting member whichconnects it with that member. It is further understood that differentfeatures from different embodiments of the invention may be combinedwithin the scope of the appended claims.

While various preferred embodiments of the present invention aredisclosed, it is to be understood that the concepts of the presentinvention are susceptible to numerous changes apparent to one skilled inthe art. Therefore, the scope of the present invention is not to belimited to the details shown and described but is intended to includeall variations and modifications which come within the scope of theappended claims.

1. An electrically variable transmission comprising: an input member toreceive power from an engine; an output member; first and secondmotor/generators; first, second and third differential gear sets eachhaving first, second and third members; said input member beingselectively connected with at least one member of said gear sets, andsaid output member being continuously connected with another member ofsaid gear sets; a first interconnecting member continuously connectingsaid first member of said first gear set with said first member of saidsecond gear set; a second interconnecting member continuously connectingsaid second member of said first gear set with said first member of saidthird gear set; a third interconnecting member continuously connectingsaid second member of said second gear set with said second member ofsaid third gear set; a fourth interconnecting member continuouslyconnecting a member of said first gear set with a stationary member;said first motor/generator being continuously connected with a member ofsaid first, second or third gear set; said second motor/generator beingcontinuously connected, or selectively connected via a dog clutch, witha member of said third gear set; a first torque transmitting deviceselectively connecting a member of said first or second gear set withsaid input member; a second torque transmitting device selectivelyconnecting a member of said third gear set with another member of saidfirst, second or third gear set or with said input member; a thirdtorque transmitting device selectively connecting a member of saidsecond or third gear set with another member of said first, second orthird gear set or with said stationary member; a fourth torquetransmitting device connected in parallel with one of said first andsecond motor/generators for selectively preventing rotation thereof; andwherein said first, second, third and fourth torque transmitting devicesare engagable to provide an electrically variable transmission with acontinuously variable range of speed ratios and up to four fixed forwardspeed ratios.
 2. The electrically variable transmission of claim 1,wherein said first, second and third differential gear sets areplanetary gear sets.
 3. The electrically variable transmission of claim2, wherein carrier members of each of said planetary gear sets aresingle-pinion carrier members.
 4. The electrically variable transmissionof claim 2, wherein at least one carrier member of said planetary gearsets is a double-pinion carrier member.
 5. The electrically variabletransmission of claim 1, wherein said first, second, third and fourthtorque transmitting devices and said first and second motor/generatorsare operable to provide five operating modes in the electricallyvariable transmission, including battery reverse mode, EVT reverse mode,reverse and forward launch modes, continuously variable transmissionrange mode, and fixed ratio mode.
 6. The electrically variabletransmission of claim 1, further comprising: a fifth torque transmittingdevice connected in parallel with the other of said first and secondmotor/generators for selectively preventing rotation thereof; andwherein said first, second, third, fourth and fifth torque transmittingdevices and said first and second motor/generators are operable toprovide five operating modes in the electrically variable transmission,including battery reverse mode, EVT reverse mode, reverse and forwardlaunch modes, continuously variable transmission range mode, and fixedratio mode.
 7. An electrically variable transmission comprising: aninput member to receive power from an engine; an output member; firstand second motor/generators; first, second and third differential gearsets each having first, second and third members; said input memberbeing selectively connected with at least one member of said gear sets,and said output member being continuously connected with another memberof said gear sets; a first interconnecting member continuouslyconnecting said first member of said first gear set with said firstmember of said second gear set; a second interconnecting membercontinuously connecting said second member of said first gear set withsaid first member of said third gear set; a third interconnecting membercontinuously connecting said second member of said second gear set withsaid second member of said third gear set; a fourth interconnectingmember continuously connecting a member of said first gear set with astationary member; said first motor/generator being continuouslyconnected with a member of said first, second or third gear set; saidsecond motor/generator being continuously connected, or selectivelyconnected via a dog clutch, with a member of said third gear set; andfirst, second, third and fourth torque transmitting devices forselectively connecting said members of said first, second or third gearsets with said input member, with said stationary member or with othermembers of said gear sets, said first, second, third and fourth torquetransmitting devices being engagable to provide an electrically variabletransmission with a continuously variable range of speed ratios and upto four fixed forward speed ratios between said input member and saidoutput member.
 8. The electrically variable transmission of claim 7,wherein said first, second and third differential gear sets areplanetary gear sets, and said first torque transmitting deviceselectively connects a member of said first or second gear set with saidinput member.
 9. The electrically variable transmission of claim 8,wherein said second torque transmitting device selectively connects amember of said third gear set with another member of said first, secondor third gear set or with said input member.
 10. The electricallyvariable transmission of claim 9, wherein said third torque transmittingdevice selectively connects a member of said second or third gear setwith said stationary member or with another member of said first, secondor third gear set.
 11. The electrically variable transmission of claim10, wherein said fourth torque transmitting device is connected inparallel with one of said motor/generators for selectively preventingrotation thereof.
 12. The electrically variable transmission of claim11, further comprising: a fifth torque transmitting device connected inparallel with the other of said motor/generators for selectivelypreventing rotation thereof.
 13. The electrically variable transmissionof claim 8, wherein carrier members of each of said planetary gear setsare single-pinion carrier members.
 14. The electrically variabletransmission of claim 8, wherein at least one carrier member of saidplanetary gear sets is a double-pinion carrier member.